Novel side chain modified Delta8(14)-15-ketosterols

Two approaches to 14,15-secoergostane intermediates for the synthesis of strophasterols

Two protected 14,15-secoergostane derivatives suitable as pivotal intermediates for the synthesis of strophasterols A and B, anti-MRSA and neuronal cell-protecting natural products bearing a recently discovered strophastane skeleton, have been synthesized by two different routes. The first approach employed an oxidative cleavage of an α-hydroxy ketone intermediate with the Jones reagent as the key step to reach the targeted secoergostane from ergosterol in ten steps. In the second approach, an unprecedented reaction cascade composed of four reactions enabled us to obtain the secoergostane more efficiently in six steps.

Human cytochrome P450scc (CYP11A1) catalyzes epoxide formation with ergosterol

Cytochrome P450scc (P450scc) catalyzes the cleavage of the side chain of both cholesterol and the vitamin D(3) precursor, 7-dehydrocholesterol. The aim of this study was to test the ability of human P450scc to metabolize ergosterol, the vitamin D(2) precursor, and define the structure of the major products. P450scc incorporated into the bilayer of phospholipid vesicles converted ergosterol to two major and four minor products with a k(cat) of 53 mol · min(-1) · mol P450scc(-1) and a K(m) of 0.18 mol ergosterol/mol phospholipid, similar to the values observed for cholesterol metabolism. The reaction of ergosterol with P450scc was scaled up to make enough of the two major products for structural analysis. From mass spectrometry, NMR, and comparison of the NMR data to that for similar molecules, we determined the structures of the two major products as 20-hydroxy-22,23-epoxy-22,23-dihydroergosterol and 22-keto-23-hydroxy-22,23-dihydroergosterol. Molecular modeling and nuclear Overhauser effect (or enhancement) spectroscopy spectra analysis helped to establish the configurations at C20, C22, and C23 and determine the final structures of major products as 22R,23S-epoxyergosta-5,7-diene-3β,20α-diol and 3β,23S-dihydroxyergosta-5,7-dien-22-one. It is likely that the formation of the second product is through a 22,23-epoxy (oxirane) intermediate followed by C22 hydroxylation with the formation of strained 22-hydroxy-22,23-epoxide (oxiranol), which is immediately transformed to the more stable α-hydroxyketone. Molecular modeling of ergosterol into the P450scc crystal structure positioned the ergosterol side chain consistent with formation of the above products. Thus, we have shown that P450scc efficiently catalyzes epoxide formation with ergosterol giving rise to novel epoxy, hydroxy, and keto derivatives, without causing cleavage of the side chain.

[Regulation of cholesterol biosynthesis and metabolism in Hep G2 cells by delta8(14)-15-ketoergostane derivatives]

The comparative study of effects of 5alpha-cholest-8(14)-en-15-on-3beta-ol (I), (22E)-5alpha-ergosta-8(14),22-dien-15-on-3beta-ol (II), (22S,23S)-22,23-oxido-5alpha-ergost-8(14)-en- 15-on-3beta-ol (III) and (22R,23R)-22,23-oxido-5alpha-ergost-8(14)-en-15-on-3beta-ol (IV) on HMG-CoA reductase, CYP27A1 and CYP3A4 genes expression in Hep G2 cells was performed. In the contrast to 15-ketocholestane derivative (I), 15-ketoergostane derivatives (II - IV) decreased the HMG- CoA reductase mRNA level; (22R,23R)-22,23-oxido-5alpha-ergost-8(14)-en-15-on-3beta-ol (IV) significantly increased CYP3A4 mRNA level (320% from control). Ketosterol (II) was found to be a more potent inhibitor of cholesterol biosynthesis in Hep G2 cells at a prolong incubation, compared with ketosterol (I). The side chain conformation of compounds (I) - (IV) was evaluated by computational modeling; the correlation between biological activity of these compounds and conformational flexibility of their side chains was found. The results obtained indicated that delta8(14)-15-ketoergostane derivatives may be used as a sterol biosynthesis and metabolism regulators in liver cells.

Metabolism of a novel side chain modified Delta8(14)-15-ketosterol, a potential cholesterol lowering drug: 28-hydroxylation by CYP27A1

The synthetic inhibitors of sterol biosynthesis, 3beta-hydroxy-5alpha-cholest-8(14)-en-15-one and 3beta-hydroxy-24S-methyl-5alpha-cholesta-8(14),22-dien-15-one, are of interest as potential cholesterol lowering drugs. Rapid metabolism of synthetic 15-ketosterols may lead to a decrease, or loss, of their potency to affect lipid metabolism. 3beta-Hydroxy-5alpha-cholest-8(14)-en-15-one is reported to be rapidly side chain oxygenated by rat liver mitochondria. In an attempt to reduce this metabolism, the novel side chain modified 15-ketosterol 3beta-Hydroxy-24S-methyl-5alpha-cholesta-8(14),22-dien-15-one was synthesized. We have examined the metabolism by recombinant human CYP27A1 of this novel side chain modified 3beta-hydroxy-24S-methyl-5alpha-cholesta-8(14),22-dien-15-one and compared the rate of metabolism with that of the previously described 3beta-hydroxy-5alpha-cholest-8(14)-en-15-one. Both sterols were found to be efficiently metabolized by recombinant human CYP27A1. None of the two 15-ketosterols was significantly metabolized by microsomal 7alpha-hydroxylation. Interestingly, CYP27A1-mediated product formation was much lower with the side chain modified 3beta-hydroxy-24S-methyl-5alpha-cholesta-8(14),22-dien-15-one than with the previously described 3beta-hydroxy-5alpha-cholest-8(14)-en-15-one. A surprising finding was that this novel side chain modified sterol was metabolized mainly in the C-28 position by CYP27A1. The data on 28-hydroxylation by human CYP27A1 provide new insights on the catalytic properties and substrate specificity of this enzyme. The finding that 3beta-hydroxy-24S-methyl-5alpha-cholesta-8(14),22-dien-15-one with a modified side chain is metabolized at a dramatically slower rate than the previously described 15-ketosterol with unmodified side chain may be important for future development of synthetic cholesterol lowering sterols.